The analogy I prefer is that Unicode-encoding is like network protocol layers. In a (very simplified) network, the goal is to present an interface of a pipeline for sending a continuous stream of bytes. To achieve this, you have a protocol like TCP, which consists of routines for transforming a series of packets running through a wire into a stream of bytes. To achieve a series of packets running through a wire, you have a protocol like Ethernet, which consists of routines for transforming electrical pulses into a series of data packets. You need both Ethernet and TCP to turn electrical pulses into a stream of continuous bytes.

Similarly, the goal of Unicode is to present an interface of a stream of abstract characters (the letter "A", the number 3, the nonbreaking space, etc.). To achieve this, you use Unicode, which consists of routines to convert a stream of arbitrarily-long numbers (packets) into abstract characters. To achieve a stream of arbitrarily-long numbers, you use an encoding such as UTF-8, which consists of routines to convert a series of bytes into a stream of arbitrarily-long numbers. Now, using an encoding and Unicode, you can convert a stream of bytes (i.e., an arbitrary file) into a series of abstract characters.